Light emitting device and light source

ABSTRACT

A light emitting device includes at least one first light emitting element to emit a first light and at least one fluorescent material to convert the first light to a second light. The second light has chromaticity existing in an enclosed area in a CIE 1931 chromaticity diagram. The CIE 1931 chromaticity diagram has a curved boundary indicating a spectral locus. The enclosed area is enclosed with a first straight line, a second straight line, a third straight line, and a curved line. The first straight line connects a first point at which x is equal to 0.666 and y is equal to 0.334 and a second point at which x is equal to 0.643 and y is equal to 0.334. The second straight line connects the second point and a third point at which x is equal to 0.576 and y is equal to 0.291. The third straight line connects the third point and a fourth point at which x is equal to 0.737 and y is equal to 0.263. The curved line connects the fourth point and the first point. The curved line is a part of the curved boundary.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

The present application claims priority under 35 U. S. C. § 119 toJapanese Patent Application No. 2018-014218, filed Jan. 31, 2018. Thecontents of this application are incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a light emitting device and a lightsource.

Discussion of the Background

Light emitting devices containing light emitting diodes (LEDs) have beenused in a wide range of applications such as for displays, warninglamps, indicators, luminaries, and so forth. Examples of such lightemitting devices include diode lamps configured to emit a color lightand include a blue light emitting diode element to emit blue light and ayellow fluorescent material to emit yellow light upon being excited bythe blue light. One example thereof is a diode lamp described inJapanese Unexamined Patent Application Publication No. 2007-088248.Also, there have been known lighting configurations for vehicle talelamps and/or brake lamps, in which, a blue light emitting diode and afluorescent material configured to convert light from the blue lightemitting diode to red light are used. One example thereof is describedin Japanese Unexamined Patent Application Publication No. 2011-204406.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a light emittingdevice includes at least one first light emitting element to emit afirst light having a first peak emission wavelength in a range of 370 nmor greater and 420 nm or less, and at least one fluorescent material toconvert the first light to a second light having a second peakwavelength in a range of 550 nm or greater and to 780 nm or less. Thesecond light has chromaticity existing in an enclosed area in a CIE 1931chromaticity diagram in which chromaticity is defined in x and ycoordinates. The CIE 1931 chromaticity diagram has an outer curvedboundary indicating a spectral locus. The enclosed area is enclosed witha first straight line, a second straight line, a third straight line,and a curved line. The first straight line connects a first point atwhich x is equal to 0.666 and y is equal to 0.334 and a second point atwhich x is equal to 0.643 and y is equal to 0.334. The second straightline connects the second point and a third point at which x is equal to0.576 and y is equal to 0.291. The third straight line connects thethird point and a fourth point at which x is equal to 0.737 and y isequal to 0.263. The curved line connects the fourth point and the firstpoint. The curved line is a part of the curved boundary.

According to another aspect of the present invention, a light sourceincludes the light emitting device, a first additional light emittingdevice having a second light emitting element made of a nitride-basedsemiconductor to emit green light, and a second additional lightemitting device having a third light emitting element made of anitride-based semiconductor to emit blue light.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic cross-sectional view showing an example of lightemitting device according to a first embodiment;

FIG. 2 is a CIE 1931 chromaticity diagram showing a range ofchromaticity coordinates of light emitted by a light emitting deviceaccording to the first embodiment;

FIG. 3 is a schematic cross-sectional view showing an example of lightemitting device according to the first embodiment;

FIG. 4 is a diagram showing emission spectra of light emitting devicesaccording to Examples 1 to 3 and Comparative Examples 1 to 3;

FIG. 5 is a diagram showing a part of emission spectra of light emittingdevices according to Examples 1 to 3 and Comparative Examples 1 to 3;

FIG. 6 is a diagram showing chromaticity coordinates of light emitted bylight emitting devices according to Examples 1 to 3 and ComparativeExamples 1 to 3;

FIG. 7 is a diagram showing color matching function of a 2-degree visualfield;

FIG. 8 is a diagram showing emission spectra of light emitting devicesaccording to Example 4 and Comparative Example 4;

FIG. 9 is a diagram showing a part of emission spectra of light emittingdevices according to Example 4 and Comparative Example 4; and

FIG. 10 is a diagram showing chromaticity coordinates of light emittedby light emitting devices according to the Example 4 and ComparativeExample 4.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

A first light emitting device (a light emitting device) according to afirst embodiment will be described by way of the Embodiments andExamples. However, the present invention is not to be limited only tothese embodiments and examples. The embodiments illustrated below areintended as illustrative of a first light emitting device to giveconcrete forms to technical ideas of the present invention, and thescope of the invention is not limited to the first light emitting deviceto those described below.

The relation between the color names and the chromaticity coordinates,the relation between the range of wavelength of light and the color nameof single color light, and the like conform to Japanese IndustrialStandard (JIS) Z8110. More specifically, the wavelengths of 380 nm to410 nm correspond to purple light, 410 nm to 455 nm correspond to bluepurple light, 455 nm to 485 nm correspond to blue light, 485 nm to 495nm correspond to blue green light, 495 nm to 548 nm correspond to greenlight, 548 nm to 573 nm correspond to yellow green light, 573 nm to 584nm correspond to yellow light, 584 nm to 610 nm correspond to yellow redlight, and 610 nm to 780 nm correspond to red light.

Also, a numerical range indicated using “to” in the presentspecification represents a range including numerical values describedbefore and after “to” as a minimum value and a maximum value,respectively. Further, when a plurality of substances that correspond toone component are present in a composition, the term “(a) content of acomponent in the composition” is referred to a total amount of theplurality of substances present in the composition, unless otherwiseindicated.

First Light Emitting Device

A first light emitting device will be illustrated below with referenceto accompanying drawings. FIG. 1 is a schematic cross-sectional viewshowing an example of light emitting device according to the firstembodiment. FIG. 2 is a CIE 1931 chromaticity diagram showing a range ofchromaticity coordinates of light emitted by a light emitting deviceaccording to the first embodiment.

The first light emitting device 101 is configured to emitshort-wavelength visible light, for example, light having a wavelengthin a range of 360 nm to 450 nm, and includes a first light emittingelement 11 of a gallium nitride-based compound semiconductor having afirst peak emission wavelength in a range of 370 nm to 420 nm, and apackage 20 where the light emitting element 11 is mounted. The package20 includes a first lead 21, a second lead 22, and a fixing part 23. Thepackage 20 is provided with a recess defined by an upward-facing surfaceand at least one lateral surface. The first lead 21 and the second lead22 are arranged to form parts of the upward-facing surface and thefixing part 23 that is electrically insulating is arranged to insulatethe first lead 21 and the second lead 22. The fixing part 23 ispreferably disposed between the first lead 21 and the second lead 22 andintegrally formed into the at least one lateral surface, but the fixingpart 23 may disposed between the first lead 21 and the second lead 23and the at least one lateral surface defining the recess may be formedwith another member. The first light emitting element 11 is mounted onthe upward-facing surface of the recess of the package 20. The firstlight emitting element 11 has positive and negative electrodes at a samesurface side, and is mounted in a face-down manner. The first lightemitting element 11 is electrically connected to the first lead 21 andthe second lead 22 by the electrically conductive member 30,respectively. The first light emitting element 11 is covered by thesealing member 50 that contains a fluorescent material 60.

Instead of face-down mounting, the first light emitting element 11 maybe mounted in a face-up manner. When a face-up mounting is employed, thefirst light emitting element 11 may be electrically connected to thefirst lead 21 and the second lead 22 by using wires in place of theelectrically conductive member 30.

The first light emitting device 101 includes a light source that mainlyincludes the first light emitting element 11 having a first peakemission wavelength in a range of 370 nm to 420 nm, and at least onefluorescent material 60 having a second peak emission wavelength in arange of 550 nm to 780 nm. In the specification, the expression “mainlyincludes” refers to inclusion of fluorescent material that contributesto light emission.

The first light emitting device 101 is configured to emit light in arange corresponding to an enclosed area in the CIE 1931 chromaticitydiagram, obtained by determining a first point at chromaticitycoordinates of x=0.666, y=0.334, a second point at chromaticitycoordinates of x=0.643, y=0.334, a third point at chromaticitycoordinates of x=0.576, y=0.291, and a fourth point at chromaticitycoordinates of x=0.737, y=0.263, then assuming a first straight linebetween the first point and a second point, a second straight linebetween the second point and the third point, and a third straight linebetween the third point and the fourth point, and, enclosing an areawith the first, second, and third straight lines and a curved linebetween the fourth point and the first point in the chromaticitydiagram. The CIE 1931 is incorporated by reference. The CIE 1931chromaticity diagram has a curved boundary indicating a spectral locus.The curved line is a part of the curved boundary. With thisconfiguration, the first light emitting device 101 that can emit lightof predetermined red color with high luminance can be provided.

The first light emitting element 11 has a first peak emission wavelengthin a range of 370 nm to 420 nm, preferably in a range of 400 nm to 415nm. The use of light at a shorter wavelength side of visible light canreduce influence of the light on the luminance. The luminous efficiencyfactor is to express a degree of sensitivity of human visual perceptionwith respect to wavelength. The human eye is sensible to light ofwavelength in a range of about 400 nm to 700 nm. In high lightconditions (i.e., in day light or other bright light), the human eye ismost sensitive to light of 555 nm in green region. For example, in highlight conditions, when the intensity of green light of wavelength 555 nmperceived by the human eye is assumed to be 100, the same of blue lightof 450 nm is about 3.8 and red light of 700 nm is about 0.4. Thus, evenwhen a predetermined amount of visible light in a range of 400 nm to 415nm has been emitted, the human eye perceive it with little intensity,such that the human eye perceive red light that is emitted from thefluorescent material 60 is emitted from the first light emitting device.Meanwhile, the first light-emitting element 11 can excite thefluorescent material 60 to emit a predetermined amount of light.Accordingly, a light emitting device of high luminance can be provided.

The first light emitting element 11 has an appropriate half value widthof the emission spectrum, which is preferably 30 nm or less. With thehalf band width of 30 nm or less, light of short wavelength side can bemade to be hardly visibly recognized.

In the emission spectrum of the first light emitting device 101, whenthe maximum intensity of the second peak emission wavelength is assumedto be 1, the relative intensity of the first peak emission wavelength tobe preferably in a range of 0.005 to 0.2, more preferably in a range of0.02 to 0.15. With a predetermined ratio of light having the first peakemission wavelength and light having the second peak emissionwavelength, the first light emitting device 101 that can emit red lightof high luminance can be provided. The first light emitting device 101that can emit red light is realized by increasing the amount of lightthat is emitted from the first light emitting element 11 and is absorbedby the fluorescent material 60, and significantly reducing the amount oflight that is emitted from the first light emitting element 11 and isdischarged to the outside from the first light emitting device 101. Ifdischarging of light from the first light emitting element 11 to theoutside is totally blocked, the amount of light discharged from thefirst light emitting device 101 to the outside decreases, and the firstlight emitting device 101 of high luminance cannot be obtained.Accordingly, when the maximum intensity at the second peak emissionwavelength is set to 1, the relative intensity at the first peakemission wavelength is preferably in a range of 0.005 to 0.2,particularly preferably in a range of 0.02 to 0.15.

The at least one fluorescent material 60 is at least one selected fromthe group consisting of a (Sr,Ca)AlSiN₃:Eu fluorescent material, aCaAlSiN₃:Eu fluorescent material, and a K₂SiF₆:Mn fluorescent material.Accordingly, the first light emitting device with high luminance can beprovided.

The at least one fluorescent material 60 is preferably a combination ofa (Sr, Ca)AlSiN₃:Eu fluorescent material and a CaAlSiN₃:Eu fluorescentmaterial. With this combination, absorption of light between the(Sr,Ca)AlSiN₃:Eu fluorescent material and the CaAlSiN₃:Eu fluorescentmaterial can be reduced, and the first light emitting device ofpredetermined brightness can be provided. That is, the peak emissionwavelength of the (Sr,Ca)AlSiN₃:Eu fluorescent material is 10 nm or morelonger than the peak emission wavelength of the CaAlSiN₃:Eu fluorescentmaterial, so that the first light emitting device 101 that can emitdeeper red light can be provided.

It is preferable that the first light emitting device 101 furtherincludes a light-reflecting member 40 covering lateral surfaces of thefirst light emitting element 11 and a sealing member 50 covering theupper surface of the first light emitting device 11 and containing thefluorescent material 60. With this arrangement, a large amount of lightemitted from the lateral surfaces of the first light emitting element 11can be directed in a front direction. Also, covering the upper surfaceof the first light emitting element 11 and the upper surface of thereflecting member 40 by the fluorescent material 60 can reduce theamount of returning light that is emitted from the first light emittingelement 11 and incident on and reflected from the fluorescent material60 and other component members toward the first light emitting element11. That is, the amount of light emitted from the first light emittingelement 101 to the outside can be reduced when the returning lightincident on the lateral surfaces of the first light emitting element 11and propagates within the first light emitting element 11.

The sealing member 50 is preferably arranged in order from the sideproximate to the first light emitting element 11, a layer containing theCaAlSiN₃:Eu fluorescent material, and a layer containing the (Sr,Ca)AlSiN₃:Eu fluorescent material. With this arrangement, the amount oflight emitted from the (Sr, Ca)AlSiN₃:Eu fluorescent material andabsorbed by the CaAlSiN₃:Eu fluorescent material can be reduced, thus,the first light emitting device 101 of higher efficiency can beprovided.

It is preferable that the sealing member 50 includes, from the sideproximate to the side distal to the first light emitting element 11, thefirst layer containing a fluorescent material and the second layercontaining a fluorescent material, with an interface between the firstlayer and the second layer. When the content amount of the fluorescentmaterial contained in the first layer is assumed to be 100%, the contentof the fluorescent material contained in the second layer is to be in arange of 1% to 60%. Providing the interface between the first layer andthe second layer can reduce the amount of light returning to the firstlayer from the second layer. Also, containing a lower content of thefluorescent material in the second layer than that in the first layerallows for an increase in the amount of light emitted from the firstlight emitting element 11 and the fluorescent material contained in thefirst layer.

The content of the fluorescent material 60 is preferably in a range of20 parts to 50 parts by weight with respect 100 parts by weight of thesealing member 50. If the fluorescent material 60 is used to increasethe amount of red light, the amount of light emitted from the firstlight emitting device 101 to the outside decreases. Thus, the contentamount of the fluorescent material 60 is preferably in the predeterminedrange.

The first light emitting element 11 is preferably a nitride-basedsemiconductor, because of its good heat resistance and good opticalresistance.

FIG. 3 is a schematic cross-sectional view showing an example of lightemitting device according to the first embodiment.

As shown in FIG. 3, it is preferable that the first light emittingdevice 101 further includes a dielectric multilayer film 70 on thesealing member 50. The light of the first light emitting element 11 thatis emitted from the first light emitting device 101 to the outside canbe returned toward the fluorescent material side by the dielectricmultilayer film 70. Thus, the first light emitting device 101 that canefficiently emit predetermined red light can be provided. For example,dispersing the fluorescent material allows for a reduction in the amountof light that is blocked by the fluorescent material contained in theupper layer, which allows for an increase in the amount of light emittedfrom the fluorescent material and discharged to the outside from thefirst light emitting device. On the other hand, this arrangement canfacilitate the propagation of light from the first light emittingelement among the fluorescent material, which may result in an increasein the amount of light leaking from the first light emitting device tothe outside. However, the light leaking to the outside can be reflected70 by the dielectric multilayer film and made incident on thefluorescent material. Thus, the amount of light emitted from the firstlight emitting element and discharged from the first light emittingdevice to the outside can be reduced.

The dielectric multilayer film 70 is preferably disposed on an uppersurface of the sealing member 50. Also, in addition to the upper surfaceof the sealing member 50, the dielectric multilayer film 70 ispreferably disposed on the upper surface of the package 20 defining arecess. Accordingly, all or most light from the first light emittingelement can be reflected at the dielectric multilayer film 70 andleakage of light emitted from the first light emitting element to theoutside of the first light emitting device can be reduced. With thedielectric multilayer film 70 provided to the first light emittingdevice, red light of high purity can be realized.

The dielectric multilayer film 70 is configured to reflect light of thefirst light emitting element and transmit light having second peakemission wavelength. The dielectric multilayer film 70 preferably has areflection spectrum that provides a reflectance of 40% or greater, morepreferably 45% or greater, to light from the first light emittingelement in a wavelength range of 370 nm to 420 nm, incident to thedielectric multilayer film 70 at an incident angle range of 0° to 85°.It is further preferable that the dielectric multilayer film 70 has areflection spectrum with a reflectance of 90% or greater, to light fromthe first light emitting element in a wavelength range of 370 nm to 420nm, incident to the dielectric multilayer film 70 at an incident anglerange of 0° to 50°.

With this arrangement, even when the light from the first light emittingelement 11 is incident to the dielectric multilayer film 70 at anincident angle other than normal (i.e., 0°), transmittance of light fromthe first light emitting element 11 can be prevented or reduced, whichallows for providing a first light emitting device 101 whose emission ofnear-ultraviolet light, violet light, or blue-violet light that isharmful to human health can be prevented or reduced.

The first light emitting device 101 can exhibit each chromaticitycoordinates at the points as described above, with a difference in therange of chromaticity coordinates at an ambient temperature of 25° C.,and the range of chromaticity coordinates at an ambient temperature of150° C., within a range of x=0.010, and y=0.010. As described above, thefirst light emitting device 101 that exhibits small change in thechromaticity in spite of a change in the ambient temperature. In theapplications requiring a certain range of chromaticity, such as warninglights and indicator lights, occurrence of large shifts in color isundesirable. Therefore, the first light emitting device 101 that canprovide small maximum allowable shifts in chromaticity can besignificantly useful.

Examples of the type of the light emitting device 101 include alamp-type and a surface-mounted type, and a chip type. Generally, theterm (a) “lamp-type” refers that a resin material forming the externalsurface of a light emitting device is formed in a lamp-shape. Forexample, a lamp-type light emitting device includes a lead member havinga cup-shape at one side, a light emitting element arranged in the cup,and a sealing resin member covering the light emitting element and aportion of the lead member. Meanwhile, a “surface-mounted type” lightemitting device refers to that a light emitting element is placed in arecess-shaped housing and resin is applied in the recess to cover thelight emitting element. The recess-shaped housing may be formed by usinga material such as thermoplastic resin, thermosetting resin, ceramics,or a metal. A “chip type” light emitting device refers to that withoutproviding a recess-shaped housing, a fluorescent material is applied ona light emitting element, and lateral surfaces of the light emittingelement, or the like is secured in place by a resin material. For a chiptype light emitting device, a layer containing a fluorescent materialcan be applied in a plate-like shape, or may be applied in a lens shape.In the description below, a surface-mounted type will be illustrated.

Light Emitting Element

The light emitting element has a peak emission wavelength in a range of370 nm to 420 nm. The use of a light emitting element that has anemission peak wavelength in the range shown above as an excitation lightsource allows for obtaining of a light emitting device to emit light ofmixed color of the light emitted from the light emitting element andfluorescent light emitted from the phosphors.

For the first light emitting element, a semiconductor light emittingelement can be preferably used. Because a semiconductor light emittingelement can provide high linearity of outputting to inputting in highefficiency, and has high tolerance to mechanical impacts and stability.For example, a semiconductor light emitting element configured to emitlight of a blue-purple color or a blue color, using a nitride-basedsemiconductor (In_(X)Al_(Y)Ga_(1-X-Y)N, 0≤X, 0≤Y, X+Y≤1) etc., can beused.

Package

A surface-mounted type package has a first lead, a second lead, and afixing part. For a surface-mounted type package, a top-view type that isused to emit light in a direction approximately perpendicular to themounting surface, or a side-view type that is used to emit light in adirection approximately in parallel to the mounting surface, is mainlyemployed, and either type can be employed in the present disclosure.

The first lead and the second lead are each made of a plate-shapedmetal. When viewed from the opening of the recess, the first lead andthe second lead are not projected outside of the fixing part, but aconfiguration in which the first lead and/or the second lead projectingoutside of the fixing part can also be employed.

Examples of preferable materials for the first lead and the second leadinclude, a metal having a thermal conductivity of about 200 W/(m·K) orgreater, a material having relatively large mechanical strength, and amaterial which can be easily processed in pressing or etching Morespecific examples of such materials include metals such as copper,aluminum, gold, silver, tungsten, iron, nickel, and alloys such asiron-nickel alloy and phosphor bronze. Also, a base material that iscovered by a metal such as silver, aluminum, or gold, having higheroptical reflectance than the base material may also be employed. For thefixing part, resin such as thermoplastic resin or thermosetting resin,inorganic material such as ceramics, a metal that is covered by aninsulating material, or the like, can be employed. Also, it ispreferable that a light-reflecting material is contained in the materialof the fixing part, for example, in the resin or the like.

Electrically Conductive Member

The electrically conductive member is configured to secure the firstlight emitting element to the package, and to electrically connect thepositive and negative electrodes of the first light emitting element tothe first lead and the second lead, respectively. For the electricallyconducting bonding member, an appropriate material can be selectedaccording to a purpose, examples thereof include electrically conductivepaste of silver, gold, palladium, or the like, and solder such astin-bismuth-based solder, tin-copper-based solder, tin-silver-basedsolder, gold-tin-based solder, or the like, a brazing material such as alow-melting-point metal.

Reflecting Member

The reflecting member covers one or more lateral surfaces of the firstlight emitting element and upper surfaces of the first and second leads.The reflecting member is preferably arranged so that at a portion incontact with the first light emitting element, the reflecting member isapproximately in a same plane or at lower than the upper surface of thefirst light emitting element. The reflecting member is preferablyarranged in contact with one or more lateral surfaces that define therecess. The reflecting member may be made of particles and preferablycontains at least one light-diffusing material selected from a groupconsisting of zirconium oxide, yttrium oxide, aluminum oxide, aluminumhydride, barium carbonate, barium sulfide, magnesium oxide, andmagnesium carbonate. The particles of the reflecting member may besecured, directly or via an adhesive material or the like, on the firstlead and the second lead.

Sealing Member

The sealing member can be made of any appropriate material that iselectrically insulating and allows the light emitted from the firstlight emitting element and the fluorescent material to pass through, andhas fluidity before it is solidified or hardened. Examples of thesealing member include thermoplastic resin, thermosetting resin, andglass. More specific examples of the thermosetting resin include epoxyresin, silicone resin, and modified silicone resin such asepoxy-modified silicone resin. Among those, a silicone resin ispreferable because of it has high heat-resistance and highlight-resistance, and exhibits a small volume contraction in solidifyingor hardening.

The sealing member preferably can disperse a fluorescent material. Aslong as the state of the dispersion is not adverse, presence of smallamount of precipitation of the fluorescent material, or occurrence ofconcentration difference in the dispersed fluorescent material can beallowed. That is, uniform dispersion of the fluorescent material byusing a sealing member having high viscosity is preferable, but instead,a sealing member having slightly lower viscosity may be employed toreduce the hardening time, while a portion of the fluorescent materialis allowed to be precipitated but most of the fluorescent material isdispersed. At the time of mixing fluorescent material particles in thesealing member, if a sealing member having a high viscosity is used, ahigher viscosity may result depending on the amount of the fluorescentmaterial, which makes it difficult to obtain uniform dispersion of thefluorescent material particles. With the use of a sealing member havinglower viscosity, a rise in the viscosity can be reduced, which allowsdispersion of higher concentration of the fluorescent materialparticles.

At the time of uniformly dispersing the fluorescent material, othercomponents such as a light diffusing material may also be included asneeded.

The sealing member can be formed with a single layer, or with aplurality of layers, such as two layers or three layers. For example,the sealing member may include a first layer proximate to the firstlight emitting element and a second layer distal to the first lightemitting element, further, an interface may be present between the firstlayer and the second layer. The first layer and the second layer may bemade of the same material. The first layer and the second layer may bemade of different materials. For example, providing a second layer thathas a refractive index greater than that of the first layer allows toreflect light emitted from the first light emitting element at theinterface between the first layer and the second layer, so that thelight from the first light emitting element can be returned to the firstlayer side, which can increase the amount of light incident on thefluorescent material. Alternatively, providing a second layer that has arefractive index smaller than that of the first layer allows toefficiently transmit light emitted from the fluorescent materialcontained in the first layer to the second layer, so that the lightextraction efficiency from the first light emitting device to theoutside can be increased.

Fluorescent Material

The fluorescent material can absorb light emitted from the first lightemitting element and emit light of different wavelength. The presentembodiment employs at least one fluorescent material that can absorblight from the first light emitting element having a first peak emissionwavelength in a range of 370 nm to 420 nm and emit light having a secondpeak emission wavelength in a range of 550 nm to 780 nm. That is, thefluorescent material emits a red light. The fluorescent material has asecond peak emission wavelength in a range of 550 nm to 780 nm, and theemission spectrum covers a range of wavelengths from 550 nm to 780 nm.The first light emitting element preferably has a second peak emissionwavelength in a range of 610 nm to 680 nm, more preferably in a range of610 nm to 650 nm. Because the luminosity efficiency factor has a peak at555 nm which decreases toward longer wavelength, and thus, a fluorescentmaterial having a second peak wavelength in a range of 610 nm to 650 nmis preferable to improve the luminance.

It is preferable that one fluorescent material is contained in thesealing member, but two or three fluorescent materials may be contained.Because, the increase in the number of fluorescent materials requiresconsideration of deterioration, change in thermal characteristics, andso forth of each fluorescent material, which increases difficulty incontrolling. Specific examples of the fluorescent materials include,SCASN-based fluorescent materials such as (Sr,Ca)AlSiN₃:Eu, CASN-basedfluorescent materials such as CaAlSiN₃:Eu, CESN fluorescent materialssuch as Ca₂Si₅N₈:Eu, (Sr,Ca)₂Si₅N₈:Eu, and KSF-based fluorescentmaterials such as K₂SiF₆:Mn. Of those, at least one SCASN-basedfluorescent material and at least one CASN-based fluorescent material,or a combination of a plurality of SCASN-based and CASN-basedfluorescent materials are preferably used. Note that among the SCASNfluorescent materials, different ratio of Sr and Ca may result differentemission color, so that fluorescent materials having a difference in thepeak emission wavelengths 5 nm or greater are determined as differentfluorescent materials.

In an emission spectrum of the first light emitting device, when amaximum intensity of the second peak emission wavelength is assumed tobe 1, a relative intensity of the first peak emission wavelength is tobe in a range of 0.005 to 0.2. The relative intensity can be adjusted bythe type and the use amount of the fluorescent material.

The content mass % of the fluorescent material can be determined bymeasuring characteristic x-rays released when a cross section of thefirst light emitting device is irradiated by electron beams, using ascanning electron microscope. For example, the measurement may beperformed by using a scanning electron microscope S-4700 manufactured byHitachi, Ltd.

In the case in which the phosphor member includes one or more othercomponents, the contents thereof can be suitably set according topurpose and the like. In view of light extraction efficiency, theaverage particle diameter of the fluorescent material is preferably in arange of 1 μm to 20 μm, more preferably in a range of 5 μm to 15 μm.

Light Diffusing Material and Other Components

A light diffusing material is preferably contained in the sealing memberto obtain more uniform dispersion of the fluorescent material in thesealing member. For the light diffusing material, silica, alumina,magnesium oxide, antimony oxide, aluminum oxide, barium sulfate,magnesium oxide, barium carbonate, barium titanate, or the like can beused, among those, silica is preferably used. The particle diameter ofsilica may be in a range of 1 to 300 μm, preferably in a range of 1 to50 μm. The refractive index of silica to be used is in a range of 1.46to 1.53, and with the use of silicone resin having a refractive index ina range of 1.54 to 1.56 for the sealing member, the reflectance can beimproved. The content of the light diffusing material may be in a rangeof 0.1 to 10 parts by weight, preferably in a range of 0.8 to 2 parts byweight, with respect to 100 parts by weight of the sealing member.

When needed, the sealing member may include one or more other componentsin addition to the fluorescent material and the light diffusingmaterial. Examples of other components include a filler material, anoptical stabilizer, a coloring agent, and an antioxidant. The fillermaterial is used with the aim to increase the strength of the fixingpart of the package, or the like, rather than aiming to reflect light.In the case where the sealing member includes one or more othercomponents, the contents thereof can be suitably set according topurpose and the like. For example, in the case of including a fillermaterial, the content of the filler material can be in a range of 0.01to 20 parts by weight with respect to 100 parts by weight of the sealingresin.

Light Source

The first light emitting device can be applied in a light source thatincludes the first light emitting device, a second light emitting device(a first additional light emitting device) having a second lightemitting element made of a nitride-based semiconductor and configured toemit green light, and a third light emitting device (a second additionallight emitting device) having a third light emitting element made of anitride-based semiconductor and configured to emit blue light. The lightsource is a so-called a three-in one light source, employing threeprimary colors of light, and is corresponding to a single pixel in adisplay image.

In the conventional light sources employing a red light emitting elementmade of GaP, GaAs, or the like, in combination of a green light emittingelement and a blue light emitting element as described above, due to adifference in thermal characteristics between GaP, GaAs, or the like,and the nitride-based semiconductors, shifts in color have been occurredas the temperature changes. When the red light emitting element made ofGaP, GaAs, or the like is used and the ambient temperature of the lightemitting element is raised from 25° C., to 150° C., occurrence of ashift in color due to a shift in the peak emission wavelength of about20 nm to 30 nm to a shorter wavelength side has been observed.

On the other hand, in a light source that includes the first lightemitting device using the first light emitting element that is anitride-based semiconductor, the second light emitting device (the firstadditional light emitting device) having the second light emittingelement made of a nitride-based semiconductor and configured to emitgreen light, and a third light emitting device (the second additionallight emitting device) having a third light emitting element made of anitride-based semiconductor and configured to emit blue light, all thelight emitting elements are made of nitride-based semiconductors andhaving common thermal characteristics. Thus, shifts in color may be verysmall even in occurrence of change in the temperature. In particular,when the first light emitting element that is a nitride-basedsemiconductor is used, and the ambient temperature of the light emittingelement is raised from 25° C., to 150° C., a shift of the peak emissionwavelength in the emission spectrum is merely 3 nm or less, and asignificant shift in color has not been observed.

Occurrence of color shifts of a light source for direct-viewapplications such as display may be a significant obstacle. Therefore,the light source according to the present embodiment can be veryadvantageous in that color shifts of the light source can besubstantially prevented.

EXAMPLES

Next, the present disclosure will be more specifically described withreference to examples, which however are not intended to limit thepresent invention.

Next, the first light emitting devices of Examples 1 to 3 andComparative Examples 1 to 3 will be described. FIG. 4 is a diagramshowing emission spectra of light emitting devices according to Examples1 to 3 and Comparative Examples 1 to 3. FIG. 5 is a diagram showing apart of emission spectra of light emitting devices according to Examples1 to 3 and Comparative Examples 1 to 3. FIG. 6 is a diagram showingchromaticity coordinates of light emitted by light emitting devicesaccording to Examples 1 to 3 and Comparative Examples 1 to 3; FIG. 7 isa diagram showing color matching function of a 2-degree visual field,which is specified by Japanese Industrial Standard (JIS) Z 8781-1 thatrefers to the CIE 1931 2-degree Standard Observer. For example, the term“2-degree visual field” is used in color determination, in which anobserver looks at a sample with 1.7 cm diameter at a distance of 50 cmfrom a direction perpendicular to the diameter of the sample todetermine a color of the sample.

Examples 1-3, Comparative Examples 1-3

Table 1 shows powder properties and luminous characteristics of thefluorescent materials A, B, and C. As the luminous characteristics ofthe fluorescent materials A to C, the chromaticity coordinates x and yof fluorescent light emitted by an excitation light of 460 nm are shown.The average particle size of each of the fluorescent materials is listedas a Fisher number measured by using a Fisher Sub-Sieve Sizer(manufactured by Thermo Fisher Scientific Co.) that employs an airpermeable method. The median particle size Dm is a volume medianparticle size measured by using a Coulter Multisizer II (manufactured byBeckman Coulter Inc.) that determines the electric resistance ofparticles.

TABLE 1 Average 460 nm-Excitation Particle Light Emission CompositionDiameter Dm Properties Formula (μm) (μm) x y Fluorescent CaAlSiN₃:Eu13.0 18.0 0.682 0.317 Material A Fluorescent CaAlSiN₃:Eu 13.0 18.0 0.6900.310 Material B Fluorescent CaAlSiN₃:Eu 12.0 16.5 0.655 0.344 MaterialC

The first light emitting devices are produced according to Examples 1 to3 and Comparative Examples 1 to 3, respectively. In the below, similarto those in the first embodiment may be appropriately omitted.

For the first light emitting element to be used in the first lightemitting devices of Examples 1 to 3, a nitride-based semiconductor lightemitting element with a first peak emission wavelength at about 405 nmis used. For the first light emitting element to be used in the firstlight emitting devices of Comparative Examples 1 to 3, a nitride-basedsemiconductor light emitting element with a first peak emissionwavelength λp at about 450 nm is used. For the fluorescent materials Aand B to be used in the first light emitting devices of Examples 1 to 3and Comparative Examples 1 to 3, fluorescent materials respectively witha second peak emission wavelength in a range of 610 nm to 750 nm areused. For the packages used in the first light emitting devices ofExamples 1 to 3 and Comparative Examples 1 to 3, NJSW172A manufacturedby Nichia Corporation are used, and for the sealing member, siliconeresin (KJR-9023NW, manufactured by Shin-Etsu Chemical Co., Ltd) is used.

The fluorescent materials A and B are used such that the mainwavelengths of the light emitted from the first light emitting devicesare respectively in a range of about 620 nm to about 640 nm,respectively. In Examples 1 to 3 and Comparative Examples 1 to 3, thefluorescent materials A and B are used in a mixture. In the presentspecification, the term “main wavelength” refers to a wavelength at apoint obtained by connecting a chromaticity point of a white light andthe chromaticity point of light emitted by each of the first lightemitting devices by a straight line, and determining the point ofintersection of an extension line of the straight line and the locus ofa monochromatic light.

The fluorescent materials A and B described above are contained in thesealing member at predetermined ratios, and mixed and dispersed, andfurther degassed, to obtain respective fluorescent material-containingresin compounds. The percentage contents of the fluorescent materialsshown in the tables are respectively weight percentages based on theweight of the sealing member as 100%.

Next, the fluorescent material-containing resin composition is injectedto enclose the first light emitting element, and heat treating isapplied at about 150° C., for four hours to harden the resincomposition. Through the steps as described above, each of the firstlight emitting devices is produced. In the first light emitting devicesof Examples 1 to 3 and Comparative Examples 1 to 3, a light reflectivematerial and a diffusing material are not added.

Table 2 shows luminous characteristics of the first light emittingdevices of Examples 1 to 3 and Comparative Examples 1 to 3.

TABLE 2 Wave- Fluo- length rescent of Light Ma- Chroma- Emit- Fluo-terial/ ticity Wave- Color ting rescent Resin Coordinates length PurityElement Material (%) x y (nm) (%) Example 1 405 nm Fluorescent 30 0.6860.301 624.6 96.1 Material A, B Example 2 405 nm Fluorescent 45 0.7000.297 626.5 99.1 Material A, B Example 3 405 nm Fluorescent 60 0.7060.293 629.6 99.6 Material A, B Compar- 450 nm Fluorescent 30 0.626 0.268494.5 78.2 ative Material Example 1 A, B Compar- 450 nm Fluorescent 450.690 0.291 632.9 94.2 ative Material Example 2 A, B Compar- 450 nmFluorescent 60 0.704 0.292 630.7 98.8 ative Material Example 3 A, B

The first light emitting devices of Examples 1 to 3 and ComparativeExamples 2 and 3 each emits predetermined red light. The light emittedfrom the first light emitting device of Comparative Example 1 is not inthe predetermined chromaticity range and has a main wavelength λdshorter than that of Example 1. With the use of the same fluorescentmaterial at a substantially the same content amount, the light emittingdevice 1 of Example 1 exhibits higher color purity compare to that ofComparative Example 1. With the use of the same fluorescent material ata substantially the same content amount, the light emitting device 1 ofExample 2 exhibits higher color purity compare to that of ComparativeExample 2. With the use of the same fluorescent material at asubstantially the same content amount, the light emitting device 1 ofExample 3 exhibits higher color purity compare to that of ComparativeExample 3. Compared to Comparative Examples 1 to 3, Examples 1 and 3require a smaller rate of fluorescent material configured to obtain redlight of the predetermined color and high color purity, which indicatesa smaller cost in manufacturing the first light emitting devices. In thepresent specification, the term “color purity” is obtained by dividing adistance between a chromaticity point of a white light and thechromaticity point of light emitted by the first light emitting deviceby a length of a straight line segment between the chromaticity point ofa white light and the locus of a monochromatic light, through thechromaticity point of light emitted from the first light emittingdevice. The reduction in the content amounts of the fluorescent materialin Examples 1 to 3 is due to that the wavelength of the light emittedfrom the light emitting element is not available in the color matchingfunction as shown in FIG. 7 and thus even the light from the lightemitting element is extracted to the outside, the light is not perceivedas color to the human eye. The color matching function is the numericaldescription of the spectral response sensitivity of the human eye anddefined as function of wavelength, which is represented by threefunctions of XYZ color system.

Example 4, Comparative Example 4

Next, the first light emitting devices of Examples 4 and ComparativeExample 4 will be described. FIG. 8 is a diagram showing emissionspectra of light emitting devices according to Example 4 and ComparativeExample 4. FIG. 9 is a diagram showing a part of emission spectra oflight emitting devices according to Example 4 and Comparative Example 4.FIG. 10 is a diagram showing chromaticity coordinates of light emittedby light emitting devices according to the Example 4 and ComparativeExample 4.

In Example 4 and Comparative Example 4, packages NJSW172A, manufacturedby Nichia Corporation are used. For the first light emitting element, alight emitting element with a first peak emission wavelength at about405 nm is used in Example 4, and a light emitting element with a firstpeak emission wavelength λp at about 450 nm is used in ComparativeExample 4. For the sealing member, silicone resin (KJR-9023,manufactured by Shin-Etsu Chemical Co., Ltd.), is used. The fluorescentmaterials A, B, and C are used such that the main wavelengths of thelight emitted from the first light emitting devices are respectively ina range of about 615 nm to about 640 nm, respectively. In Example 4 andComparative Example 4, the fluorescent materials A, B, and C are used ina mixture, respectively. The fluorescent materials A, B and C describedabove are contained in the sealing member at predetermined ratios, andmixed and dispersed, and further degassed, to obtain respectivefluorescent material-containing resin compounds. The percentage contentsof the fluorescent materials shown in the tables are respectively weightpercentages based on the weight of the sealing member as 100%.

Next, the fluorescent material-containing resin composition is injectedto enclose the first light emitting element, and heat treating isapplied at about 150° C., for four hours to harden the resincomposition. Through the steps as described above, each of the firstlight emitting devices is produced. In the first light emitting devicesof Example 4 and Comparative Example 4, a light reflecting material anda light diffusing material are not added.

Table 3 shows luminous characteristics of the first light emittingdevices of Example 4 and Comparative Example 4.

TABLE 3 Wave- Fluo- length rescent Chroma- of Light Material/ Luminousticity Emitting Fluorescent Resin Efficiency Coordinates ElementMaterial (%) (lm/W) x y Example 4 405 nm Fluorescent 26.8-30 7.9 0.6850.301 Material A, B Comparative 450 nm Fluorescent   50-75 7.5 0.6850.301 Example 4 Material A, B, C

The first light emitting devices of Example 4 and Comparative Example 4emit predetermined red light, respectively. In order to obtainsubstantially the same chromaticity point, Example 4 requires a smalleramount of the fluorescent material compared to that of ComparativeExample 4, the first light emitting device can be manufactured with asmaller cost. Also, at the same chromaticity point, compared toComparative Example 4, Example 4 exhibits a higher luminous efficiencyof 0.4 (lm/W) and greater brightness. Compared to Comparative Example 4,Example 4 requires a smaller amount of the fluorescent material, canefficiently irradiate the fluorescent material with light from the firstlight emitting element, and can efficiently extract light from thefluorescent material to the outside without being interrupted by otherparticles of the fluorescent material, and thus, a high luminousefficiency can be obtained.

The first light emitting devices according to the embodiments of thepresent invention can be applied in wide range of fields such as generallighting, on-vehicle lighting, decorative lighting, warning lamps, andindicators.

It is to be understood that although the present invention has beendescribed with regard to preferred embodiments thereof, various otherembodiments and variants may occur to those skilled in the art, whichare within the scope and spirit of the invention, and such otherembodiments and variants are intended to be covered by the followingclaims.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A light emitting device comprising: at least onefirst light emitting element to emit a first light having a first peakemission wavelength in a range of 370 nm or greater and 420 nm or less;and at least one fluorescent material to convert the first light to asecond light having a second peak emission wavelength in a range of 550nm or greater and 780 nm or less, the second light having chromaticityexisting in an enclosed area in a CIE 1931 chromaticity diagram in whichchromaticity is defined in x and y coordinates, the CIE 1931chromaticity diagram having a curved boundary indicating a spectrallocus, the enclosed area being enclosed with a first straight line, asecond straight line, a third straight line, and a curved line, thefirst straight line connecting a first point which x is equal to 0.666and y is equal to 0.334 and a second point at which x is equal to 0.643and y is equal to 0.334, the second straight line connecting the secondpoint and a third point at which x is equal to 0.576 and y is equal to0.291, the third straight line connecting the third point and a fourthpoint at which x is equal to 0.737 and y is equal to 0.263, the curvedline connecting the fourth point and the first point, the curved linebeing a part of the curved boundary.
 2. The light emitting deviceaccording to claim 1, wherein in an emission spectrum of the lightemitting device, a ratio of an intensity of the first peak emissionwavelength to a maximum intensity of the second peak emission wavelengthis in a range of 0.005 to 0.20.
 3. The light emitting device accordingto claim 1, wherein the at least one fluorescent material includes atleast one selected from the group consisting of a (Sr, Ca)AlSiN3:Eufluorescent material, a CaAlSiN3:Eu fluorescent material, and aK2SiF6:Mn fluorescent material.
 4. The light emitting device accordingto claim 1, wherein the at least one fluorescent material includes acombination of the (Sr, Ca)AlSiN3:Eu fluorescent material and theCaAlSiN3:Eu fluorescent material.
 5. The light emitting device accordingto claim 1 further comprising: a light-reflecting member coveringlateral surfaces of the first light emitting element, and a sealingmember covering an upper surface of the first light emitting element andcontaining the at least one fluorescent material.
 6. The light emittingdevice according to claim 5, wherein the sealing member includes a firstlayer containing the CaAlSiN3:Eu fluorescent material and a second layercontaining the (Sr, Ca)AlSiN3:Eu fluorescent material, the first lightemitting element being closer to the first layer than to the secondlayer.
 7. The light emitting device according to claim 5, wherein thesealing member includes a first layer containing the fluorescentmaterial a second layer containing the fluorescent material, and aninterface interposed between the first layer and the second layer, thefirst light emitting element being closer to the first layer than to thesecond layer, and a ratio of a first content of the fluorescent materialin the second layer to a second content of the fluorescent material inthe first layer is in a range of 1% to 60%.
 8. The light emitting deviceaccording to claim 5, wherein the content of the fluorescent material inthe sealing member is in a range of 20 to 50 parts by weight withrespect to 100 parts by weight of the sealing member
 50. 9. The lightemitting device according to claim 1, wherein the first light emittingelement is made of a nitride-based semiconductor.
 10. The light emittingdevice according to claim 1 further comprising a dielectric multilayerfilm on the sealing member.
 11. The light emitting device according toclaim 10, wherein the dielectric multilayer film has a reflectance of40% or greater of a light having a wavelength ranging from 370 nm to 420nm, the light being incident on the dielectric multilayer film at anincident angle range of 0° to 85°.
 12. The light emitting deviceaccording to claim 10, wherein the dielectric multilayer film has areflectance of 90% or greater of a light having a wavelength rangingfrom 370 nm to 420 nm, the light being incident on the dielectricmultilayer film at an incident angle range of 0° to 50°.
 13. The lightemitting device according to claim 1, wherein both an x-difference and ay-difference in chromaticity coordinates between the second light at anambient temperature of 25° C. and the second light at an ambienttemperature of 150° C. are within a range of 0.010.
 14. A light sourcecomprising: the light emitting device according to claim 1; a firstadditional light emitting device having a second light emitting elementmade of a nitride semiconductor to emit green light; and a secondadditional light emitting device having a third light emitting elementmade of a nitride semiconductor to emit blue light.